Aluminum alloy heat exchanger

ABSTRACT

An aluminum alloy heat exchanger with aluminum alloy tubes is provided by assembling and brazing. A coating which includes from 1 to 5 g/m 2  of Si powder, from 3 to 20 g/m 2  of Zn containing flux, and from 0.2 to 8.3 g/m 2  of binder is formed on the aluminum alloy tubes. The fins contain Zn and 0.8 to 2.0% by mass of Mn, Si in a ratio of 1/2.5 to 1/3.5 relative to the Mn, and less than 0.30% by mass of Fe. A fillet is formed between the tube and the aluminum alloy fin after brazing, and a primary crystal portion is formed in the fillet. A eutectic crystal portion is formed in a portion other than the primary crystal portion, and the electric potential of the primary crystal portion is equal to or higher than the electric potential of the aluminum alloy fin.

FIELD OF THE INVENTION

The present invention relates to an aluminum alloy heat exchanger, andspecifically relates to an aluminum alloy heat exchanger in whichdetachment of fins from tubes can be suppressed.

Priority is claimed on Japanese Patent Application No. 2010-45734 filedon Mar. 2, 2010, the content of which is incorporated herein byreferences.

BACKGROUND ART

A heat exchanger made of aluminum alloy (aluminum alloy heat exchanger)is mainly constituted of tubes, fins, and header pipes that are brazedto each other. Conventionally, extruded tubes having a surface thermallysprayed with Zn, fins composed of a (three layered) brazing sheet havingclad layers of Al—Si alloy filler on both sides has been widely used incombination in the heat exchanger.

Recently, world-wide production of inexpensive, high-quality, andhigh-performance product has been realized utilizing a combination of aextruded tube with a surface coating for brazing composed of Si powder,Zn-containing flux, and binder, and fins made of a bare unclad sheet(single layer sheet that does not have a brazing filler).

In the heat-exchanger made of the latter combination, sacrificial anodefins containing Zn are used as the fins, and thereby suppressingoccurrence and progress of corrosion of the tubes by sacrificial anodecorrosion protection effect of the fins. In addition, Zn contained inthe flux of the coating for brazing diffuses during brazing and forms asacrificial anode layer on the surface of the tube. As a result,progress of corrosion generated on the tube is suppressed, and leakageof refrigerant due to corrosion of the tube is prevented.

In addition, during the brazing process, liquid brazing filler that isformed by reaction of the coating for brazing and the tube flows towardsthe joint of the fin and the tube and joins the fin and the tube byforming a fillet. Thus, high heat-exchanging performance can beobtained.

Based on the above-described background art, in Patent Reference 1, theinventors proposed a heat exchanger tube with a coating for brazingformed on the outer surface of the tube, where Si powder in an amount of1 to 5 g/m² and Zn-containing flux in an amount of 5 to 20 g/m² werecontained in the coating.

Since the Si powder and the Zn-containing flux are mixed in the coatingof the proposed tube, Si powder fuses during brazing and forms a liquidbrazing filler, and Zn in the flux diffuses in the liquid brazing fillerand is spread uniformly on the surface of the tube. Since the diffusionrate of Zn in a liquid phase such as the liquid brazing filler isremarkably higher than the diffusion rate of Zn in solid phase, asubstantially uniform Zn concentration is achieved on the surface of thetube. By this process, a uniform sacrificial anode layer is formed onthe surface of the tube, thereby improving the corrosion resistance ofthe heat exchanger tube.

PRIOR ART REFERENCE Patent Reference

-   Patent Reference 1: Japanese Unexamined Patent Application, First    Publication No. 2004-330233.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the heat-exchanger tube of the above-described constitution, partialcontent of Zn included in the flux of the coating for brazing flows tothe joint with the fin in accordance with flow of the liquid brazingfiller formed during the brazing process. Therefore, a fillet formed inthe joint of the tube and the fin contains diffused Zn.

As a result, the fillet in the joint is occasionally corrodedselectively, thereby causing a possibility of detachment of the fin fromthe tube, where the heat exchanger is used for example in a region of avery severe corrosion environment.

As a performance of heat exchanger of this type, it is important tomaintain high heat exchanging performance for a long period of time. Forthis purpose, it is necessary to prevent leakage of refrigerant causedby corrosion and to maintain joining of the fin and the tube for a longperiod of time.

Separation of the fin in the heat exchanger may cause a problem inperformance of the heat exchanger tube, for example, by deterioration ofheat exchanging performance, and shortening of anti-corrosion lifetimeof the heat exchanger (tube) due to reduction of the corrosionprotection effect of the fin.

On the other hand, if the amount of Zn added to the fin is increased soas to reduce the potential of the fin to be lower than that of thefillet, corrosion rate of the fin is increased remarkably, and therebycausing a possibility of partial loss of fins due to fin-wear due tocorrosion. As a result, there has been a possibility of reduction ofheat exchanging performance.

Based on the above-described circumstance, an object of the presentinvention is to provide a heat exchanger made of aluminum alloy in whichhigh joining ratio of fins and tubes is exhibited, corrosion of the tube(if there is) is controlled to shallow level, and separation of the finis inhibited.

Solution of the Problems

An aluminum alloy heat exchanger of the present invention is an aluminumalloy heat exchanger formed by assembling and brazing an aluminum alloytube and an aluminum alloy fin to each other, wherein a coating forbrazing comprising 1 to 5 g/m² of Si powder, 3 to 20 g/m² of Zncontaining flux, and 0.2 to 8.3 g/m² of binder is formed on the surfaceof the aluminum alloy tube; the fin contains 0.8 to 2.0% by mass of Mn,Si in an amount of 1/2.5 to 1/3.5 of Mn content; less than 0.30% by massof Fe, and Zn in an amount that is controlled in relation with theamount of the Zn containing flux in the coating for brazing to be in aregion enclosed by points A, B, C, D, E, F of FIG. 5; a filletcomprising brazing filler of the coating for brazing (brazing fillerformed by melting of the coating for brazing and solidification of themelt) is formed between the tube and the aluminum alloy fin after thebrazing; a primary crystal portion that joins the fin and the tube isformed in the fillet; a eutectic crystal portion is formed in a portionother than the primary crystal portion; and electric potential of theprimary crystal portion is set equal to electric potential of thealuminum alloy fin or higher than the electric potential of the aluminumalloy fin.

In the above-described aluminum alloy heat exchanger, the aluminum alloytube may be composed of less than 0.1% by mass of Cu, 0.1 to 0.6% bymass of Si, 0.1 to 0.6% by mass of Fe, 0.1 to 0.6% by mass of Mn, andthe balance consisting of Al and unavoidable impurities.

In the above-described aluminum alloy heat exchanger, the aluminum alloytube may further contain at least one of 0.005 to 0.2% by mass of Ti and0.05 to 0.2% by mass of Cr.

In the above-described heat exchanger, the aluminum alloy fin maycontain one or two or more selected from 0.05 to 0.2% by mass of Zr,0.01 to 0.2% by mass of V, 0.05 to 0.2% by mass of Ti, and 0.01 to 0.2%by mass of Cr.

Effect of the Invention

According to the aluminum alloy heat exchanger of the present invention,by controlling the amount of Zn included in the coating for brazingformed on the surface of the tube and the amount of Zn contained in thealuminum alloy fin to appropriate amounts respectively, it is possibleto diffuse Zn into the fillet formed after the brazing appropriately. Asa result, it is possible to provide an aluminum alloy heat exchanger inwhich progress of corrosion of the fillet is suppressed even when theheat exchanger is used for a long time under a corrosive environment,and separation of a fin does not occur easily.

Since the fin is not separated easily in the aluminum alloy heatexchanger of the present invention, it is possible to achievesacrificial anode corrosion protection of the tube by the fin for arelatively long period of time. As a result, it is possible to prolonganti-corrosion service life of the tube compared to the conventionalcase.

Primary crystal portion to join the fin and tube is generated andeutectic crystal portion is generated in the other portion in the filletformed after the brazing of the aluminum alloy heat exchanger of thepresent invention. Where the coating for brazing has the above-describedcomposition and the aluminum alloy fin has the above-describedcomposition, electric potential of the primary crystal portion of thefillet is equal to or higher than the electric potential of the aluminumalloy fin that is close to the fillet. As a result, the primary crystalportion of the fillet is made resistant to corrosion. By this effect, itis possible to prevent separation of fins.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is a front view that shows an example of a constitution of a heatexchanger according to the present invention.

FIG. 2 is a partial enlarged view of a heat exchanger according to thepresent invention and shows a state after assembling and brazing headerpipes, tubes and fins.

FIG. 3 is a partial enlarged view that shows a state in which headerpipes, tubes, and fins are assembled before brazing

FIG. 4 is a partial enlarged cross-sectional view of a heat exchanger ofthe present invention for explaining occurrence of primary crystalportion and eutectic crystal portion in the joint where a fin and a tubeare joined via a fillet.

FIG. 5 is a graph that shows relation between an amount of Zn containedin aluminum alloy fin and an amount of Zn-containing flux included inthe coating for brazing in the heat exchanger according to the presentinvention.

FIG. 6 is a side view that schematically shows a joint of a tube and afin in an example of a heat exchanger according to the presentinvention.

FIG. 7 is a side view that schematically shows a structure of an examplein which separation of fin occurred after the corrosion.

FIG. 8 is a schematic view that shows lateral cross section of a tubeused in an example of the present invention.

MODE FOR CARRYING OUT THE INVENTION

An aluminum alloy heat exchanger of the present invention is an aluminumalloy heat exchanger formed by assembling and brazing an aluminum alloytube and an aluminum alloy fin to each other, wherein a coating forbrazing comprising 1 to 5 g/m² of Si powder, 3 to 20 g/m² of Zncontaining flux, and 0.2 to 8.3 g/m² of binder is formed on the surfaceof the aluminum alloy tube; the fin contains 0.8 to 2.0% by mass of Mn,Si in an amount of 1/2.5 to 1/3.5 of Mn content; less than 0.30% by massof Fe, and Zn in an amount that is controlled in relation with theamount of the Zn containing flux in the coating for brazing to be in aregion enclosed by points A, B, C, D, E, F of FIG. 5; a filletcomprising brazing filler of the coating for brazing is formed betweenthe tube and the aluminum alloy fin after the brazing; a primary crystalportion that joins the fin and the tube is formed in the fillet; aneutectic crystal portion is formed in a portion other than the primarycrystal portion; and electric potential of the primary crystal portionis set equal to electric potential of the aluminum alloy fin or higherthan the electric potential of the aluminum alloy fin.

Where the electric potential of the primary crystal portion is equal tothe electric potential of the aluminum alloy fin, it is acceptable if asubstantially equal potential is achieved. For example, electricpotential of the primary crystal portion may be lower than the electricpotential of the aluminum alloy fin if the difference of the electricpotentials is within 5 mV.

The inventors investigated a mechanism of corrosion in joints ofconstituent members of aluminum alloy heat exchanger that was mainlyconstituted of tubes, fins, and header pipes, and that was produced bybrazing of these constituents. As a result, it was found that theabove-described problems could be solved by examining a relationshipbetween the amount of Zn-containing flux in the coating for brazing andthe amount of Zn in the fin, and controlling the two amounts to be inappropriate relationship to prevent separation of a fin from the tubedue to selective corrosion of a fillet at the joint of the fin.

The selective corrosion of fillet is caused by lower (basic) electricpotential of the fillet than the electric potential of the sacrificialanode fin. Therefore, corrosion mechanism of a fillet was investigatedin detail.

As a result of the investigation, it was discovered that the fillet 9formed in the joint of fin and tube 3 was constituted of primary crystalportions 9 a, 9 b and eutectic crystal portion 9 c in theabove-described type of heat exchanger formed by braze-joining.

The primary crystal portions 9 a, 9 b are portions of a fillet 9 thathave solidified firstly from the liquid brazing filler during cooling inthe brazing process. The portion which has remained to be molten duringthe formation of the primary crystal portion constitutes the eutecticcrystal portion 9 c in accordance with progress of cooling. As a resultof examination by the inventors, it was found that the primary crystalportions 9 a, 9 b thus formed in the fillet 9 had lower (basic) Znconcentration than that of the eutectic crystal portion 9 c, therebyachieving high (noble) electric potential. That is, in the fillet 9, theeutectic crystal portion 9 c has higher Zn concentration and is easilycorroded than the primary crystal portions 9 a, 9 b, and the primarycrystal portions 9 a, 9 b have lower Zn content and are not easilycorroded compared to the eutectic crystal portion 9 c.

As a result of investigation by the inventors, it was found that, evenwhen the fillet containing Zn was corroded selectively, joining of a finand a tube in a heat exchanger could be maintained for a long period oftime if the primary crystal portion of low Zn concentration and highelectric potential was protected from corrosion by selective(preferential) corrosion of a eutectic crystal portion 9 c of thefillet.

In addition, it was found that the primary crystal portions 9 a, 9 c ofthe fillet 9 could be made resistant to corrosion by controlling theelectric potential of the primary crystal portions 9 a, 9 b to be equalto or higher than that of the fin 4 acting as sacrificial anode in thevicinity of joint of the fin 4 and the tube 3, and that theabove-described conditions could be realized by controlling each of theamount of Zn-containing flux in the coating for brazing and the amountof Zn in the fin 4 having a composition for efficiently exhibitingsacrificial anode effect.

Hereafter, the present invention is explained in detail based on theembodiment shown in the drawings.

FIG. 1 shows an embodiment of a heat exchanger according to the presentinvention. The heat exchanger 100 is mainly constituted of: header pipes1, 2 that are spaced apart to left side and right side in parallelarrangement; a plurality of flat tubes 3 that are arranged in parallelwith a interval in the space between the header pipes and that arejoined with right angle to the header pipes 1, 2; and corrugated fins 4provided to each of the tubes. The header pipes 1, 2, tubes 3, and fins4 are constituted of the below-described aluminum alloys.

More specifically, a plurality of slits 6 are formed with apredetermined interval along longitudinal direction in the sides of theheader pipes 1, 2 opposed to each other, and the header pipes 3 arebridged by the tubes 3 by inserting ends of each tube 3 to the opposedslits 6 of the header pipes 1, 2. Fins 4 are arranged between theplurality of tubes 3, 3 that are disposed between the header pipes 1, 2with a predetermined interval. These fins 4 are brazed to a front(upper) surface or a back (lower) surface of the tube 3. As shown inFIG. 2, a fillet 8 is formed of brazing filler in each of the portionswhere the ends of the tubes 3 are inserted to the slits 6 of the headerpipes 1, 2, and the tubes 3 are brazed to the header pipes 1, 2. Ridgesof the corrugated fins 4 are opposed to the front surface or the backsurface of the tubes 3 and fillets formed of brazing filler are formedtherebetween. Thus, fins 4 are brazed to the front surface and the backsurface of the tubes 3.

As explained in the below description of the production method, the heatexchanger 100 of this form is produced by forming a heat exchangerassembled body 101 as shown in FIG. 2 by assembling header pipes 1, 2, aplurality of tubes 3 disposed between the header pipes 1, 2, and aplurality of fins, and subjecting the assembled body 101 to brazing.

At a state before the brazing, the front surface and the back surface ofthe tube 3 to which the fin 4 is joined are coated with a coating forbrazing including 1 to 5 g/m² of Si powder, 3 to 20 g/m² ofZn-containing flux (KZnF₃), and 0.2 to 8.3 g/m² of binder (for example,an acrylic based resin).

The tube 3 of the present embodiment is constituted as a flat multi-porttube that has a plurality of path formed inside and has a flat frontsurface (upper surface) 3A and a flat back surface (lower surface) 3B,and side surfaces adjacent to the front surface 3A and the back surface3B. As an embodiment, a coating 7 for brazing is formed on each of thefront surface 3A and the back surface 3B of the tube before the brazing.

Hereafter, a composition constituting the coating for brazing isexplained.

<Si Powder>

Si powder reacts with Al as a component of the tube 3 and forms abrazing filler that joins the fin 4 and the tube 3. The Si powder meltsin the brazing process and forms liquid brazing filler. Zn in the fluxdiffuses in the liquid brazing filler and is spread uniformly over thesurface of the tube 3. Since diffusion rate of Zn in the liquid brazingfiller, a liquid phase, is remarkably higher than the diffusion rate ofZn in a solid phase, substantially uniform Zn concentration is achievedon the surface of the tube 3. Thus formed uniform Zn diffusion layerimproves corrosion resistance of the tube 3.

Coated Amount of Si Powder: 1 to 5 g/m².

Where the coated amount of Si powder is smaller than 1 g/m², brazabilityis deteriorated. On the other hand, where the coated amount of Si powderexceeds 5 g/m², due to formation of excessive brazing filler, Zn tendsto concentrate in the fillet, and unreacted Si residue occurs, resultingin large corrosion depth and failing to achieve intended effect forpreventing separation of fins. Therefore, the amount of Si powderincluded in the coating is set to be 1 to 5 g/m². Preferably, the amountof Si powder is 1.5 to 4.5 g/m², and more preferably, 2.0 to 4.0 g/m².As an example, the particle size of the Si powder is controlled to be 15μm or less in D(99), where D(99) denotes a diameter at which cumulativeparticle size distribution from smaller size reaches 99% by volume.

<Zn Containing Flux>

Zn containing flux has an effect of forming Zn diffused layer on thesurface of the tube 3 during brazing process and improves the corrosionresistance. In addition, the flux has an effect of removing oxide on thesurface of the tube during the brazing process to enhance spreading andwetting of the brazing filler, thereby improving brazability. Since theZn containing flux has higher activity than the flux not containing Zn,it is possible to achieve satisfactory brazability even where relativelyfine Si powder is used.

Coated Amount of Zn Containing Flux: 3 to 20 g/m²

Where the coated amount of Zn-containing flux is smaller than 3 g/m², asufficient Zn diffused layer is not formed and corrosion resistance ofthe tube 3 is deteriorated. In addition, defective brazing is caused byinsufficient deformation and removal of the surface oxide film of amember to be brazed (tube 3). On the other hand, where the coated amountexceeds 20 g/m², Zn concentrates remarkably in the primary crystalportion 9 a, 9 b of the fillet, deteriorating the corrosion resistanceof the fillet and accelerating separation of the fin. Therefore, coatedamount of Zn-containing flux is controlled to be 3 to 20 g/m².Preferably, amount of Zn-containing flux in the coating is 4 to 18 g/m²,more preferably, 5 to 15 g/m².

The amount of Zn-containing flux in the coating 7 for brazing has strongcorrelation with the Zn content in the fin 4. The relationship isexplained in detail in the below description.

Preferably, KZnF₃ is used as a main component of the Zn-containing flux.Alternatively, it is possible to use mixed type flux in which KZnF₃ ismixed with, where necessary, Zn-free flux such as K₁₋₃AlF₄₋₆,Cs_(0.02)K₁₋₂AlF₄₋₅, AlF₃, KF, and K₂SiF₆. The amount of coating iscontrolled such that the amount of Zn-containing flux is in the range of3 to 20 g/m².

Preferably, amount of Zn in the Zn-containing flux is in the range of 35to 45% by mass.

<Binder>

In addition to the Si powder and the Zn-containing flux, the coatingcomposition includes binder. Preferably, acrylic based resin can beapplied as an example of the binder.

Coated Amount of Binder: 0.2 to 8.3 g/m²

Where the amount of binder in the coating is smaller than 0.2 g/m²,workability (exfoliation resistance of the coating) is deteriorated. Onthe other hand, if the amount of binder in the coating exceeds 8.3 g/m²,brazability is deteriorated. Therefore, the coated amount of binder iscontrolled to be 0.2 to 8.3 g/m². In general, the binder is lost byevaporation by the heating during the brazing process. A preferableamount of binder in the coating is 0.4 to 6.0 g/m², and more preferably0.5 to 5.0 g/m².

A method of applying the brazing composition comprising the Si powder,flux, and binder is not limited in the present invention. It is possibleto use appropriate method, for example, selected from a spray method, ashower method, a flow-coater method, a roll-coater method, a brashpainting method, a dipping method, and a electrostatic painting method.The area for coating the brazing composition may be the whole surface ofthe tube or a partial surface of the tube. It is acceptable if thesurface region of the tube 3 required for brazing the fin is coated withthe composition.

The tube 3 is made of an aluminum alloy that is composed of, in % bymass, less than 0.1% of Cu and the balance being aluminum andunavoidable impurities. Where necessary, the aluminum alloy of the tubemay further contains, in % by mas, 0.1 to 0.6% of Si, 0.1 to 0.6% of Fe,and 0.1 to 0.6% of Mn. The tube 3 is produced by extrusion process ofthe aluminum alloy.

Hereafter, a reason for limiting constituent elements of aluminum alloyof the tube is explained.

<Cu: Less than 0.1%>

Cu is an element that has influence on the corrosion resistance of thetube 3. Although no problem is caused where the Cu content is less than0.1%, Cu content exceeding 0.1% tends to deteriorate corrosionresistance. On the other hand, addition of Cu improves the strength ofthe tube 3. Therefore, Cu may be added in an amount of less than 0.1%.

<Mn: 0.1 to 0.6%>

Mn is an element that improves corrosion resistance and mechanicalstrength of the tube 3. Mn also improves extrudability during theextrusion process. Further, Mn has an effect of suppressing fluidity ofthe liquid brazing filler and suppress the difference in Znconcentration between the fillet and the tube surface.

Where the Mn content is less than 0.1%, effect of improving corrosionresistance and the strength is insufficient, and the effect ofsuppressing fluidity of liquid brazing filler is reduced. On the otherhand, where the Mn is contained in excess of 0.6%, the extrudability isdeteriorated due to increase of extrusion pressure. Therefore, in thepresent invention, the Mn content is preferably controlled to be 0.1 to0.6%. A more preferable Mn content is 0.15 to 0.5%, and more preferably,0.2 to 0.4%.

<Si: 0.1 to 0.6%>

Si is an element that has an effect of improving strength and corrosionresistance like as Mn.

Where the Si content is smaller than 0.1%, the effect of improving thecorrosion resistance and the strength cannot be achieved sufficiently.On the other hand, a Si content exceeding 0.6% deterioratesextrudability. Therefore, in the present invention, the Si content inthe tube 3 is preferably controlled to be 0.1 to 0.6%. A more preferableSi content is 0.15 to 0.5%, and more preferably, 0.2 to 0.45%.

<Fe: 0.1 to 0.6%>

Fe is an element that has an effect of improving the strength and thecorrosion resistance like as Mn.

Where the Fe content is smaller than 0.1%, the effect of improving thecorrosion resistance and the strength cannot be achieved sufficiently.On the other hand, the Fe content exceeding 0.6% deterioratesextrudability. Therefore, in the present invention, Fe content in thetube 3 is preferably controlled to be 0.1 to 0.6%. A more preferable Fecontent is 0.15 to 0.5%, and more preferably, 0.2 to 0.4%.

<Ti: 0.005 to 0.2%, Cr: 0.05 to 0.2%>

Ti and Cr are elements which may be contained where necessary, andimprove corrosion resistance of the tube 3. However, where the contentsof these elements exceeds the above-described range, the extrudabilityof the alloy tends to be deteriorated.

Next, fin 4 is explained.

The fin 4 joined to the tube 3 is made of an aluminum alloy thatcontains, in % by mass, Mn: 0.8 to 2.0%, Si: 1/2.5 to 1/3.5 of the Mncontent, Zn: an amount defined by the range enclosed by points A, B, C,D, E, F shown in FIG. 5, Fe: less than 0.3%, and further contains, wherenecessary, one or two or more selected from Zr: 0.05 to 0.2%, V: 0.01 to0.2%, Ti: 0.05 to 0.2%, Cr: 0.01 to 0.2%, and the balance being Al andunavoidable impurities. Explanation for the region enclosed by points A,B, C, D, E, F shown in FIG. 5 will be described afterwards.

In the preparation of fin 4, aluminum alloy having the above-describedcomposition is formed of melt in accordance with a common method, and isworked to a corrugated shape through hot-rolling, cold rolling, or thelike. The production method of the fin 4 is not limited in the presentinvention, and known methods may be applied in the production of fin 4.Hereafter, limitation of constituent elements of the aluminum alloy ofthe fin is explained.

<Mn: 0.8 to 2.0%>

Mn improves high temperature strength and room temperature strength ofthe fin 4.

Where the Mn content is less than 0.8%, the effect of improving hightemperature strength and room temperature strength cannot be achievedsufficiently. On the other hand, where the Mn content exceeds 2.0%,sufficient workability cannot be obtained in the preparation process ofthe fin 4. Therefore, the Mn content in the alloy of constituting thefin is controlled to be 0.8 to 2.0%. A preferable Mn content is 0.9 to1.9%, more preferably, 1.0 to 1.8%.

<Si: 1/2.5 to 1/3.5 of the Mn Content>

Where the alloy contains Si, Si forms compounds with Mn and exhibits theabove-described effect of Zn and effect of improving strength. Where thecontent of Si exceeds the above-described range, separation of the fintends to occur. A preferable Si content is 1/2.6 to 1/3.6 of the Mncontent, more preferably, 1/2.8 to 1/3.2 of the Mn content.

<Fe: Less than 0.30%>

Where the amount of Fe exceeds 0.30%, workability in the preparationprocess of the fin 4 and the corrosion resistance of the fin 4 aredeteriorated. On the other hand, Fe improves the high temperaturestrength and room temperature strength of the Fin 4. Therefore, Fe maybe contained in the fin 4 in an amount more than 0% and less than 0.30%.

<Zn Content>

By making the fin 4 contain Zn, it is possible to reduce the electricpotential of the fin 4 and to provide sacrificial anode corrosionprotection effect to the fin 4.

It is necessary to control the amount of Zn in the fin 4 to be, in % bymass, not less than 0.5% and not more than 6%. Where the Zn content inthe fin 4 is less than 0.5%, separation of fin 4 tends to occur. WhereZn content exceeds 6%, corrosion resistance of the fin 4 itself tends tobe deteriorated.

Further, based on the below described reason, Zn content of the fin 4 isrequired to satisfy the specific range enclosed by points A, B, C, D, E,and F shown in FIG. 5 in correlation with the above-described amount ofZn-containing flux.

FIG. 4 shows a partial enlarged view indicating a state where a fillet 9is formed in the joint of the tube 3 and the fin 4 after the brazing. Inthe fillet 9, primary crystal portion 9 a is formed in the vicinity ofthe tube 3, primary crystal portion 9 b is formed in the vicinity of thefin 4, and eutectic crystal portion 9 c is formed in the region betweenthe primary crystal portions 9 a and 9 b. This occurrence is explainedas follows.

The coating 7 for brazing is molten by the heating in the time ofbrazing, and forms liquid brazing filler that flows towards the joint offin 4 and tube 3 and forms the fillet 9.

Therefore, during the brazing, fillet 9 has a liquid state, and fin 4and the tube 3 have solid state.

The liquid fillet 9 is solidified in the subsequent cooling process.Firstly, portions in contact with solid fin 4 and tube 3 start tosolidify while crystallizing primary crystals, and form the primarycrystal portions 9 a, 9 b. Finally, the portion apart from the fin 4 andthe tube 3 is solidified forming the eutectic crystal portion 9 c.

Therefore, in the metal texture shown by the fillet, the center portion4 a at which the tube 3 and the fin 4 is mostly closed is almostcomposed of the primary crystal portions 9 a, 9 b, and volume of theeutectic crystal portion 9 c increases towards the periphery of thefillet where the tube 3 and the fin 4 are spaced apart. In addition,since component of the liquid brazing filler formed by the heatingduring the brazing partially diffuses to the surface of the tube 3 andto the surface of the fin 4, the primary crystal portion 9 a occurs in astate slightly eroding the surface of the tube 3 from the lower end ofthe fillet 9, and the primary crystal portion 9 b occurs in a stateslightly eroding the surface of the fin 4 from the upper end of thefillet 9.

In the present invention, based on the observation of theabove-described separated formation of the primary crystal portions 9 a,9 b, and the eutectic crystal portion in the fillet 9, the followingfinding was obtained. It is effective to diffuse a appropriate amount ofZn in the primary crystal portions 9 a, 9 b in order to inhibitseparation of the fin 4 effectively. In the present embodiment, it isimportant to control the amount of Zn containing flux in the coating 7for brazing and the Zn content in the fin 4 to be in specificrelationship based on the above-described finding.

Specifically, where the amount of Zn containing flux (unit: g/m²) isshown by the horizontal axis, and the Zn content (unit: % by mass) inthe fin 4 is shown by the vertical axis as shown in FIG. 5, it isnecessary to control the amount Zn containing flux and the Zn content inthe fin 4 to be in the range enclosed by points A, B, C, D, E, and F,where A denotes the amount of the Zn containing flux: 3 g/m² and the Zncontent in the fin 4: 0.5% by mass, B denotes the amount of the Zncontaining flux: 10 g/m² and the Zn content in the fin 4: 2% by mass, Cdenotes the amount of the Zn containing flux: 20 g/m² and the Zn contentin the fin 4: 3% by mass, D denotes the amount of the Zn containingflux: 20 g/m² and Zn content in the fin 4: 6% by mass, E denotes theamount of the Zn containing flux: 10 g/m² and Zn content in the fin 4:5% by mass, and F denotes the amount of the Zn containing flux: 3 g/m²and the Zn content in the fin 4: 3% by mass.

By controlling the amount of Zn containing flux and the Zn content inthe fin 4 to be in the range enclosed by the points A, B, C, D, E, and Fshown in FIG. 5, it is possible to diffuse appropriate amount of Zn inthe primary crystal portions 9 a, 9 b of the fillet, and to make theprimary crystal portions 9 a, 9 b resistant to corrosion.

In the range enclosed by the points A, B, C, D, E, and F shown in FIG.5, the most preferable range is the triangle range enclosed by thepoints G, I, and H, where G denotes the amount of the Zn containingflux: 3 g/m² and the Zn content in the fin 4: 2.6% by mass, I denotesthe amount of the Zn containing flux: 15 g/m² and the Zn content in thefin 4: 2.6% by mass, and H denotes the amount of the Zn containing flux:15 g/m² and the Zn content in the fin 4: 5% by mass. Next to theabove-described range enclosed by the points G, H, and I, the trianglerange enclosed by the points G, J, and K is preferable, where G denotesthe amount of the Zn containing flux: 3 g/m² and the Zn content in thefin 4: 2.6% by mass, J denotes the amount of the Zn containing flux: 3g/m² and the Zn content in the fin 4: 1.6% by mass, and K denotes theamount of the Zn containing flux: 7.5 g/m² and the Zn content in the fin4: 2.6% by mass.

<Zr: 0.05 to 0.2%>

Zr is an element which may be contained in the fin 4 where necessary,and improves the high temperature strength and the room temperaturestrength of the fin 4 like as Fe.

Where the amount of Zr is less than 0.05%, it is impossible to achievethe effect of improving high temperature strength and room temperaturestrength. On the other hand, where the Zr content exceeds 0.2%,workability in preparation process of the fin is deteriorated.Therefore, the Zr content in the present embodiment can be controlled tobe in the range of not less than 0.05% and not more than 0.2%.

<V: 0.01 to 0.2%>

V is an element which may be contained in the fin 4 where necessary, andimproves high temperature strength and room temperature strength of thefin 4 like as Fe.

Where the amount of V is less than 0.01%, it is impossible to achievethe effect of improving high temperature strength and room temperaturestrength. On the other hand, where the V content exceeds 0.2%,workability in preparation process of the fin is deteriorated.Therefore, the V content in the present embodiment can be controlled tobe in the range of not less than 0.01% and not more than 0.2%. Apreferable V content is 0.05 to 0.18%, and more preferably, 0.10 to0.15%.

<Cr: 0.01 to 0.2%>

Cr is an element which may be contained in the fin 4 where necessary,and improves the high temperature strength and the room temperaturestrength of the fin 4 like as Fe.

Where the amount of Cr is less than 0.01%, it is impossible to achievethe effect of improving the high temperature strength and the roomtemperature strength. On the other hand, where the Cr content exceeds0.2%, the workability in the preparation process of the fin isdeteriorated. Therefore, the Cr content in the present embodiment can becontrolled to be in the range of not less than 0.01% and not more than0.2%. A preferable Cr content is 0.05 to 0.18%, and more preferably,0.10 to 0.15%.

In the present embodiment, one or two or more of Zr, V, Ti, and Cr maybe contained where necessary.

Next, the header pipe 1 is explained.

As shown in FIG. 2 and FIG. 3, the header pipe 1 preferably has a threelayered structure composed of core member layer 11, sacrificial anodelayer 12 formed in the outer periphery of the core member, and brazingfiller layer 13 formed in the inner periphery of the core member.

By forming the sacrificial anode layer 12 in the outer periphery of thecore member layer 11, it is possible to achieve corrosion protectioneffect by the header pipe 1 in addition to the corrosion protectioneffect by the fin 4. Therefore, it is possible to enhance the effect ofsacrificial anode corrosion protection of the tube 3 in the vicinity ofthe header pipe 1.

Preferably, the core member 11 is constituted of an Al—Mn based alloy.

For example, it is preferable that the alloy contains 0.05 to 1.50% ofMn, and may further contain additional elements selected from 0.05 to0.8% of Cu, and 0.05 to 0.15% of Zr.

The sacrificial anode layer 12 formed in the outer periphery of the coremember layer 11 is preferably constituted of an aluminum alloy composedof 0.6 to 1.2% of Zn, and the balance being Al and unavoidableimpurities. The sacrificial anode layer 12 is formed integral with thecore member layer by clad-rolling.

The structure and composition of the header pipe 1 explained in thepresent embodiment is one of examples. The structure and composition ofthe header pipe 1 applied in the present embodiment may be selected fromthose applied in general heat exchangers.

A method of producing a heat exchanger 100 mainly constituted of theabove-explained header pipes 1, 2, tubes 3 and fins 4 is explained inthe following.

FIG. 3 is a partial enlarged view of a heat exchanger assembly(assembled body of heat exchanger elements) 101 that shows a state inwhich header pips 1, 2, tube 3, and fins 4 are assembled using the tubes3 coated with a coating for brazing on the surface to be joined with thefin 4. The figure shows a state before brazing by heating. In the heatexchanger assembly shown in FIG. 3, an end of the tube 3 is inserted tothe slit formed in the header pipe 1 so as to install the tube.

When the heat exchanger assembly constituted of header pipes 1, 2, tubes3, and fins 4 as constructed as shown in FIG. 3 is heated to atemperature not lower than melting point of the brazing filler and iscooled after the heating, as shown in FIG. 2, brazing filler layer 13and the coating 7 for brazing are molten and the header pipe 1 and thetube 3, the tube and the fin 4 are joined respectively. Thus, a heatexchanger 100 having a constitution as shown in FIG. 1 and FIG. 2 isobtained. At that time, the brazing filler layer 13 in the innerperiphery of the header pipe 1 is molten and flows to the vicinity ofthe slit 6 and forms a fillet 8 thereby joining the header pipe 1 andthe tube 3. In addition, the coating 7 for brazing on the surface of thetube 3 is molten and flows to the vicinity of the fin 4 by capillaryforce and forms a fillet 9 thereby joining the tube 3 and the fin 4.

In the time of brazing, the coating 7 for brazing and the brazing fillerlayer 13 are molten by heating to an appropriate temperature in anappropriate atmosphere such as inert atmosphere. Then, the activity ofthe flux is enhanced, and Zn in the flux precipitates to the surface ofthe member (tube 3) to be brazed, and is diffused to the direction ofwall-thickness of the tube. In addition, the flux decomposes oxide filmsof both of the brazing filler surface and surface of the member to bebrazed, thereby enhancing wetting of the brazing filler and the memberto be brazed.

Conditions of brazing are not particularly limited. For example, thebrazing may be performed by controlling the interior of the furnace tobe nitrogen atmosphere, heating the heat exchanger assembly to a brazingtemperature (substantial attainment temperature) of 580 to 620° C. withheating rate of not smaller than 5° C./minute, maintaining the assemblyat the brazing temperature for 30 seconds or longer, and cooling theassembly while controlling the cooling rate from the brazing temperatureto 400° C. to 10° C./minute or more.

In the time of brazing, partial portions of the matrices of the aluminumalloys constituting the tube 3 and the fin 4 react with the compositionin the coating 7 for brazing applied on the surface of the tube 3 andform a brazing filler thereby brazing the tube 3 and the fin 4.

On the surface of the tube 3, Zn in the flux diffuses in the brazingprocess and make the surface of the tube 3 to be basic compared to theinterior of the tube 3. In the fillet 9, the Zn concentration in theprimary crystal portions 9 a and 9 b is lower than that of the eutecticcrystal portion 9 c, thereby providing a noble electric potential to theprimary crystal portions 9 a and 9 b compared to the eutectic crystalportion 9 c in the fillet 9. As a result, the primary crystal portions 9a, 9 b are made resistant to corrosion

Further, since the relationship between the amount of Zn-containing fluxin the coating 7 for brazing and the Zn content in the fin 4 iscontrolled to be in the range enclosed by the points A, B, C, D, E, andF as described above, the primary crystal portions 9 a and 9 b are madeto have noble electric potential compared to the fin 4. Therefore, theprimary crystal portions 9 a, 9 b are not easily corroded in theachieved structure. In addition, it is possible to control such thatexcessive Zn content is not diffused to the primary crystal portions 9a, 9 b in the time of brazing. Therefore, electric potential of theprimary crystal portions 9 a and 9 b is made higher than the electricpotential of the aluminum alloy fin 4.

According to the present embodiment, satisfactory brazing is performedwhile avoiding residual Si powder in the brazing process. The fillet 9is securely formed between the tube 3 and the fin 4, and the primarycrystal portions 9 a, 9 b are made resistant to corrosion.

In the thus obtained heat exchanger 100, an appropriate Zn layer isformed on the surface of the tube 3 and pitting corrosion is prevented.In addition, corrosion of the primary crystal portions 9 a, 9 b of thefillet is suppressed, and joining of the tube 3 and the fin 4 can bemaintained for a long time. As a result, satisfactory heat exchangingperformance is maintained.

EXAMPLE

Al alloys for tube each having a composition shown in Table 1 and Alalloys for fin each having a composition shown in Table 2 were preparedfrom molten alloys.

After a heat treatment for homogenization of the Al alloy for tube, aflat tube 30 having a lateral cross sectional shape (a wall thickness t:0.30 mm, a width W: 18.0 mm, a total thickness T: 1.5 mm, and a cornercurvature radius: 0.75 mm) as shown on FIG. 8 was prepared by hotextrusion of the Al alloy.

After a heat treatment for homogenization of the Al alloy for fin, aplate of 0.08 mm in thickness was obtained by hot-rolling and coldrolling the alloy. By corrugate working of the plate, the fin 40 asshown in FIG. 6 was prepared.

Next, brazing filler composition was roll-coated on the surface of thetube 30 and was dried.

The brazing composition is a paint comprising Si powder (2.8 μm inD(50)), flux (KZnF₃: 3.0 μm in D(50), where D(50) is a diameter at whichcumulative particle size distribution from smaller size reaches 50%),binder (acrylic resin), and solvent (including alcohol group such asisopropyl alcohol). The mixed ratio in each of the brazing compositionwas controlled such that the amount of each component in the coating forbrazing after painting and drying has a value as shown in Table 3, Table4, and Table 5.

The tube 30 and fin 40 were assembled as shown in FIG. 6 as a partialsection of a heat exchanger, and brazing was performed by heating theassembly to 600° C., maintaining the assembly at that temperature for 2minutes, and subsequently cooling the assembly.

In each case, brazing was performed in nitrogen atmosphere.

The tube and fin after the brazing were subjected to corrosion test ofSWAAT for 30 days. After the corrosion test, maximum corrosion depthformed of the tube was measured. In addition, the corrosion product wasremoved after the corrosion testing and area ratio (%) of a portion 45where the fin was separated or absent as shown in FIG. 7 was determined.

Separation ratio (%) of the fin is a value obtained by (total area ofseparation ratio of fins after the corrosion test: total area of theportion shown by symbol 45 in FIG. 7)/(total area of the fin beforecorrosion: area of regions L₁+L₂+L₃ shown in FIG. 6)×100.

Electric potential of the primary crystal portion of the fillet, theelectric potential of the fin, the corrosion depth of the tube, and theseparation ratio of the fins for each of samples No. 1 to 57 after thebrazing are shown in Table 6, Table 7, and Table 8.

TABLE 1 Mn Si Fe Cu Cr Ti (mass %) (mass %) (mass %) (mass %) (mass %)(mass %) Al tube 1 0.3 0.4 0.3 0.05 — — balance tube 2 0.3 0.4 0.3 0.15— — balance tube 3 0.3 0.4 0.3 0.05 0.15 — balance tube 4 0.3 0.4 0.30.05 — 0.15 balance tube 5 0.3 0.4 0.3 0.05 0.10 0.10 balance

TABLE 2 Mn Si Fe Zn Zr, V, Ti, Cr Fin No. (mass %) (mass %) (mass %)(mass %) (mass %) Al Remarks 1 1.5 0.5 0.15 0.3 balance Zn: less thanlower limit 2 1.5 0.5 0.15 0.5 V: 0.05 balance Zn: lower limite 3 1.50.5 0.15 1.0 balance 4 1.0 0.3 0.25 1.6 Zr: 0.05 balance 5 1.5 0.5 0.151.6 balance 6 1.5 0.5 0.15 2.0 balance 7 1.2 0.4 0.15 2.6 Zr: 0.1, Ti:0.1 balance 8 1.5 0.5 0.15 2.6 balance 9 1.8 0.6 0.20 3.0 balance 10 1.50.5 0.15 3.0 balance 11 1.5 0.5 0.15 3.5 balance 12 1.5 0.5 0.15 4.0balance 13 1.5 0.5 0.15 5.0 balance 14 1.5 0.5 0.15 5.5 balance 15 1.50.5 0.15 6.0 Cr: 0.15 balance Zn: upper limit 16 1.5 0.5 0.15 2.6balance Zn exceeds upper limit 17 1.5 0.5 0.40 2.6 balance Fe exceedsupper limit 18 1.5 0.5 0.29 2.6 balance Fe: upper limit 19 1.5 0.6 0.202.6 balance Si: upper limit 20 1.5 0.43 0.20 2.6 balance Si: lower limit21 1.5 0.75 0.20 2.6 balance Si exceeds upper limit 22 1.5 0.40 0.20 2.6balance Si is less than lower limit 23 2.0 0.7 0.20 2.6 balance Mn:upper limit 24 0.8 0.3 0.20 2.6 Zr: 0.2 balance Mn: lower limit 25 2.20.7 0.20 2.6 balance Mn: exceeds upper limit 26 0.6 0.2 0.20 2.6 Zr:0.15 balance Mn: less than lower limit

TABLE 3 Zn content Sample Coating for brazing (g/m²) in Fin No. Tube No.Fin No. Si powder Binder Zn flux (mass %) 1 1 4 1.5 1.0 2 1.6 2 1 9 1.51.0 2 3.0 3 1 1 2.0 1.0 3 0.3 4 1 2 2.0 1.0 3 0.5 5 1 3 2.0 1.0 3 1.0 61 4 2.0 1.0 3 1.6 7 1 6 2.0 1.0 3 2.0 8 1 8 2.0 1.0 3 2.6 9 1 9 2.0 1.03 3.0 10 1 12 2.0 1.0 3 4.0 11 1 5 2.5 1.0 5 1.6 12 1 6 2.5 1.0 5 2.0 131 7 2.5 1.0 5 2.6 14 1 10 2.5 1.0 5 3.0 15 1 5 3.0 1.5 7.5 1.6 16 1 83.0 1.5 7.5 2.6 17 1 9 3.0 1.5 7.5 3.0 18 1 11 3.0 1.5 7.5 3.5

TABLE 4 Zn content Sample Coating for brazing (g/m²) in Fin No. Tube No.Fin No. Si powder Binder Zn flux (mass %) 19 1 5 3.0 2.0 10 1.6 20 1 63.0 2.0 10 2.0 21 1 7 3.0 2.0 10 2.6 22 1 9 3.0 2.0 10 3.0 23 1 12 3.02.0 10 4.0 24 1 13 3.0 2.0 10 5.0 25 1 14 3.0 2.0 10 5.5 26 1 11 3.0 2.012 3.5 27 1 6 3.5 3.0 15 2.0 28 1 7 3.5 3.0 15 2.6 29 1 9 3.5 3.0 15 3.030 1 13 3.5 3.0 15 5.0 31 1 15 3.5 3.0 15 6.0 32 1 12 3.5 3.5 18 4.0 331 8 4.0 4.5 20 2.6 34 1 10 4.0 4.5 20 3.0 35 1 15 4.0 4.5 20 6.0 36 1 154.0 8.0 20 6.0 37 1 16 4.0 4.5 20 6.5 38 1 11 4.0 4.5 21 3.5 39 1 14 4.04.5 21 5.5

TABLE 5 Zn content Sample Coating for brazing (g/m²) in Fin No. Tube No.Fin No. Si powder Binder Zn flux (mass %) 40 1 17 3.0 1.5 7.5 2.6 41 118 3.0 1.5 7.5 2.6 42 1 19 3.0 1.5 7.5 2.6 43 1 20 3.0 1.5 7.5 2.6 44 121 3.0 1.5 7.5 2.6 45 1 22 3.0 1.5 7.5 2.6 46 1 23 3.0 1.5 7.5 2.6 47 124 3.0 1.5 7.5 2.6 48 1 25 3.0 1.5 7.5 2.6 49 1 26 3.0 1.5 7.5 2.6 50 27 2.5 1.0 5 2.6 51 3 7 2.5 1.0 5 2.6 52 4 7 2.5 1.0 5 2.6 53 5 7 2.5 1.05 2.6 54 1 6 0.5 1.0 5 2.0 55 1 6 5.5 1.0 5 2.0 56 1 5 3.0 Not 7.5 1.6used 57 1 5 3.0 8.5 7.5 1.6

TABLE 6 Electric potential of primary Electric crystal portion potentialCorrosion Separation Sample of fillet of Fin depth of ratio of No. (mVvs SCE) (mV vs SCE) tube (μm) fin (%) 1 −810 −840 135 50 2 −810 −900 12520 3 −820 −760 85 90 4 −820 −820 80 60 5 −820 −830 80 55 6 −820 −840 8050 7 −820 −850 75 45 8 −820 −860 75 20 9 −820 −900 75 20 10 −820 −930 7010 11 −830 −845 70 55 12 −830 −850 65 45 13 −830 −885 65 30 14 −830 −91565 15 15 −845 −845 70 60 16 −845 −860 65 40 17 −845 −900 65 30 18 −845−920 65 20

TABLE 7 Electric potential of primary Electric crystal portion potentialCorrosion Separation Sample of fillet of Fin depth of ratio of No. (mVvs SCE) (mV vs SCE) tube (μm) fin (%) 19 −855 −845 80 95 20 −855 −850 7065 21 −855 −885 65 40 22 −855 −900 65 40 23 −855 −930 65 30 24 −855 −95065 60 25 −855 −950 65 70 26 −875 −920 65 40 27 −890 −850 75 95 28 −890−885 70 65 29 −890 −900 65 50 30 −890 −950 65 40 31 −890 −960 65 75 32−910 −940 65 50 33 −920 −860 70 95 34 −920 −915 65 65 35 −920 −960 60 6536 −920 −960 70 65 37 −920 −980 70 85 38 −960 −920 70 85 39 −960 −950 7080

TABLE 8 Electric potential of primary Electric crystal portion potentialCorrosion Separation Sample of fillet of Fin depth of ratio of No. (mVvs SCE) (mV vs SCE) tube (μm) fin (%) Remarks 40 −845 −860 75 70 Fin: Feexceeds upper limit 41 −845 −860 70 60 Fin: upper limit of Fe 42 −845−860 70 60 Fin: upper limit of Si 43 −845 −860 70 60 Fin: lower limit ofSi 44 −845 −830 75 70 Fin: Si exceeds upper limit 45 −845 −835 75 70Fin: Si is less than lower limit 46 −845 −850 70 60 Fin: upper limit ofMn 47 −845 −865 70 60 Fin: lower limit of Mn 48 −845 −825 75 70 Fin: Mnexceeds upper limit 49 −845 −865 75 60 Fin: Mn is less than lower limitFin has insufficient strength 50 −830 −885 110 40 tube 2 51 −830 −885 6030 tube 3 52 −830 −885 60 30 tube 4 53 −830 −885 55 30 tube 5 54 −830−850 75 95 Si powder is less than lower limit 55 −830 −850 95 70 Sipowder exceeds upper limit 56 −845 −845 135 75 binder is less than lowerlimit 57 −845 −845 145 95 binder exceeds upper limit

Based on the constitutions of each samples shown in Tables 3, 4, 5 andthe results shown in Tables 6, 7, 8, it was found that each of samples(No. 4 to 9, 11 to 18, 20 to 24, 26, 28 to 30, 32, and 34 to 36) inwhich the amount of Zn-containing flux of the coating for brazing andthe Zn content in the fin were controlled on the range enclosed by thepoints A, B, C, D, E, and F shown in FIG. 5 in accordance with theregulation of the present invention, showed smaller maximum corrosiondepth compared to the samples (No. 1 to 3) having the amount of Zncontaining flux or Zn content of the fin outside the range enclosed byA, B, C, D, E, F of FIG. 5, and also showed smaller separation ratio offin after 30 days of SWAAT test compared to the samples (No. 10, 19, 25,27, 31, 33, 38, 39) outside the regulated range.

The sample No. 54 shown in Table 5 and Table 8 having insufficientamount of Si powder and the sample No. 55 shown in Table 5 and Table 8having an excessive amount of a Si powder both showed a high separationratio of fin.

The sample No. 56 shown in Table 5 and Table 8 not including binder andthe sample No. 57 shown in Table 5 and Table 8 including excessivebinder both showed deep corrosion depth of the tube and a highseparation ratio of fin.

Based on the constitutions of each samples shown in Table 3, Table 4,Table 5, and on the results shown in Table 6, Table 7, and Table 8, itwas discovered that the below described conditions had some influence onthe conditions for regulating the amount of Zn-containing flux in thecoating for brazing and the Zn content of Fin to be in the rangeenclosed by the points A, B, C, D, E, and F shown in FIG. 5.

Cu content of the tube 2 shown in Table 1 was 0.15% that exceeded thelimit of 0.1%, and the sample No. 50 shown in Table 4 using the tube 2showed relatively deep corrosion depth.

While fin of sample No. 25 shown in Table 2 had a larger Mn content thanthe range of the present invention, and the fin of sample No. 26 had asmaller Mn content, sample No. 48 and 49 of Table 5 and Table 8 usingthose fins showed high separation ratio of fins. While fin of sample No.21 shown in Table 2 had a larger Si content than the range of thepresent invention, and the fin of sample No. 22 had smaller Si content,sample No. 44 and 45 of Table 5 and Table 8 using those fins showed highseparation ratio of fins. The fin of sample No. 17 of Table 2 had asmaller Fe content than the range of the present invention, and thesample No. 40 of Table 5 and Table 8 using this fin showed a highseparation ratio of fin. The fin of sample No. 16 of Table 2 had asmaller Zn content than the range of the present invention, and thesample No. 37 of Table 4 and Table 7 using this fin showed a highseparation ratio of fin.

As explained above, based on the constitution of each samples shown inTable 3, Table 4, and Table 5 and the results shown in Table 6, Table 7and Table 8, it was made clear that a heat exchanger that satisfied theconditions according to the present invention could provide a heatexchanger that had excellent corrosion resistance and separation of afin did not easily occur after a corrosion resistance test.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a heatexchanger in which separation of a fin from the tube does not easilyoccur and that has excellent corrosion resistance.

The invention claimed is:
 1. An aluminum alloy heat exchanger formed byassembling and brazing one or more aluminum alloy tubes and one or morealuminum alloy fins to each other, wherein a coating for brazingcomprising from 1 to 5 g/m² of Si powder, from 3 to 20 g/m² of Zncontaining flux, and from 0.2 to 8.3 g/m² of binder is formed on asurface of the aluminum alloy tube; wherein the aluminum alloy fincomprises aluminum and from 0.8 to 2.0% by mass of Mn, Si in a ratio of1/2.5 to 1/3.5 relative to Mn, less than 0.30% by mass of Fe, and Zn inan amount that is controlled in relation with the amount of the Zncontaining flux in the coating for brazing to be in a region enclosed bypoints A, B, C, D, E, and F of FIG. 5; wherein a fillet comprisingbrazing filler of the coating for brazing is formed between the tube andthe aluminum alloy fin which are in physical contact after the brazing;wherein a primary crystal portion that joins the fin and the tube isformed in the fillet; wherein a eutectic crystal portion is formed in aportion other than the primary crystal portion; and an electricpotential of the primary crystal portion is set equal to or higher thanan electric potential of the aluminum alloy fin.
 2. The aluminum alloyheat exchanger according to claim 1, wherein the aluminum alloy tubecomprises Al and less than 0.1% by mass of Cu, from 0.1 to 0.6% by massof Si, from 0.1 to 0.6% by mass of Fe, and from 0.1 to 0.6% by mass ofMn.
 3. The aluminum alloy heat exchanger according to claim 2, whereinthe aluminum alloy tube further comprises from 0.005 to 0.2% by mass ofTi and/or from 0.05 to 0.2% by mass of Cr.
 4. The aluminum alloy heatexchanger according to any one of claims 1 to 3, wherein the aluminumalloy fin further comprises one or more selected from 0.05 to 0.2% bymass of Zr, from 0.01 to 0.2% by mass of V, from 0.05 to 0.2% by mass ofTi, and from 0.01 to 0.2% by mass of Cr.